In conventional North American electrical connectors, a female plug receptacle is designed or adapted to receive a male plug having two straight prongs, and, usually, a grounding pin. The male plug prong may be polarized, in accordance with standard practice, or they may be of the same size.
When such a connection is made, there exists the possibility that, when longitudinal stress is applied thereto, the male and female connectors may disconnect. This is especially true where one of the connectors, usually the female, is one end of an extension cord, or where, for example, the cord is an elongated attachment to a power tool and is terminated by a male plug. In such case, the disconnect is a nuisance at the very least, and potentially dangerous where power to the tool or other device is essential. Thus, for example, if the powered equipment is a hedge trimmer or lawn mower, it is necessary to stop the work to make a re-connect to the power source, which is usually terminated at its cord end with a female plug. In some cases, the disconnect may not be complete, and the prongs are slightly bared but power is still being transmitted, a real danger of electric shock can be created, especially where the grass or ground is damp.
It has been recognized in the prior art that these problems exist, and numerous arrangements have been proposed for overcoming them, substantially all such arrangements having a locking mechanism for locking the power source cord, usually terminated in a standard female connector to the power receiving tool or cord, terminated in a male connection. The standard North American male plug connector has, as pointed out hereinbefore, two flat, parallel blades, each of which has a small diameter hole spaced from the plug face at a set distance, or a small range of distance. It is a feature of most of the prior art arrangements that some means is provided for anchoring the female member terminating the power source cord to one or both of the holes.
In U.S. Pat. No. 5,921,797 of Forrester such an arrangement is shown wherein the female plug includes a mechanism for locking the connectors together by releasably engaging the holes in the male member blades. The female portion of the connector comprises a two part housing and a cap therefor which is bolted to the housing, with movable actuating and locking collars between the cap and the housing. The assembly is quite complex, with an extremely large member of individual parts, at least ten of which are movable in connecting and disconnecting the male plug therefrom. The extensive list of parts requires columns 2, 3, and 4 of the patent, and serves to emphasize the complexity of the structure.
There are numerous other prior art arrangements which depend upon engagement of the holes in the male prongs to lock the male plug to the female receptacle. See, for example, U.S. Pat. Nos. 4,319,797 of Qtaui et al., 4,932,886 of Glaser, and 5,286,213 of Altergott et al. In most prior art mechanism, the female plug terminating the power cord itself has the locking mechanism therein, and thus the arrangement is not adaptable to other power cord arrangements, such as connection of an extension cord between the power source cord and the cord of the power consuming mechanism or tool.